It has long been a practice in the building industry to attempt to waterproof the outer surface of walls and horizontal structures, such as the upper level of an underground parking garage, intended for subterranean installations. Cement block walls are quite porous and subject to seepage of water therethrough. Poured concrete walls are also porous, although to a lesser extent than the block walls. To maintain the interior of the structure dry and comfortable and to maintain the structural integrity of such walls it is essential that waterproofing be applied to the walls.
One common waterproofing technique is to coat the entire outer surface of the subterranean wall with sheets of bituminous mastic. Adhering water-impervious sheets of rubber or plastic materials to the walls is also a common waterproofing method.
Another technique which is quite effective to seal subterranean walls is the application of a layer of bentonite clay to the wall surface. This highly colloidal clay possesses the capacity to swell and gelatinize upon contact with water, thereby producing an effective water barrier. The clay is thus activated by water seeping through the soil surrounding the building structure. However, after constant exposure to flowing water, the bentonite tends to wash away.
Application of bentonite clay to wall structures is facilitated by fabricating panels in which the clay is held between water permeable sheets of paper, or the like, which are in turn fastened to the outer surface of the wall. U.S. Pat. No. 3,186,896, granted on June 1, 1976, to A. G. Clem for "Moisture Impervious Panel" discloses a bentonite clay panel for that purpose. There, two water permeable sheets are joined by a corrugated structure and the interstitial spaces are filled with the clay.
U.S. Pat. No. 3,561,177, granted on Feb. 9, 1971, to I. T. Agro, et al. for "Building Component" discloses another form of bentonite clay panel in which the clay is carried in pockets formed in a plastic carrier sheet with a rear facing permeable surface sheet covering the otherwise open cups or pockets and lying between those pockets and the wall of the protected structure. The invention depends upon water or moisture existing between the wall of the protected structure and the system of the invention to penetrate the backing sheet to expand the bentonite clay. This patent also teaches the difference between and availability of a swelling and nonswelling version of bentonite clay.
U.S. Pat. No. 3,888,087 granted to Bergsland on June 10, 1975, suggests that vertical channel protrusions along the edges of adjacently mounted sheets might be interlocked, but does not suggest or teach any sealing means therein.
These various waterproofing techniques have been effective to prevent seepage of water into and through subterranean walls. However, even with a wall that is initially waterproof, ground water seepage can cause a build-up of hydrostatic pressure against the wall which can result in severe structural damage to the waIl. The counter-measure for hydrostatic pressure is the provision of a system for draining ground water away from the subterranean walls. Although drainage can be provided by means of an aggregate fill of the excavation outside the walls, that method is both costly and time consuming.
Recently, draining panels have been developed which are designed to be attached to the outer surface of a subterranean wall to permit ground water to flow along the face of the wall to a drain pipe located at the foundation of the wall.
Examples of such draining panels can be found in U.S. Pat. Nos. 3,654,765, granted on Apr. 11, 1972, to K. A. Healy, et al. for "Subterranean Wall Drain," No. 4,490,072, granted on Dec. 25, 1984, to J. Glasser for "Drainage Device", and No. 4,574,541, granted Mar. 11, 1986, to H. P. Raidt, et al. for "Foundation-Drainage Panel". The drainage panels disclosed in these three patents differ somewhat from each other, but basically they comprise a shaped core which provides vertical passages for the flow of water down the face of the wall, on at least one side of the panel, and a fabric or screen cover on one face of the panel to prevent soil from entering and clogging the drainage passages. The panels are designed to be used with a perforated drain pipe positioned at the lower end thereof for conveying away ground water diverted from the wall by the panel.
Mirafi Inc., Charlotte, North Carolina, manufactures a line of products under its trademark, "Miradrain." "Miradrain 6000" is a non-permeable plastic sheet formed with round protrusions on a first side which are bridged by a filtering material attached at the apexes of the protrusions. The product is intended for application with the open side of the protrusions placed against a subterranean wall and the filter fabric side against the back filled earth. Fluid flow is in all directions around the protrusions. There is no means suggested for sealing the edges of these panels for waterproofing purposes, but it is suggested that the panels may be mechanically interlocked by engaging a plurality of the protrusions in one panel into the back side of the protrusions in an adjacent panel. Another product of Mirafi Inc., is "Miradrain 4000," similar to "Miradrain 6000," but having round protrusions on both sides of the panel wherein the protrusions on one side are offset from those on the other. Filter fabric is applied to both sides at the flat mesa-like apexes of the protrusions. This configuration allows free water flow on either side of the panel.
Another drainage panel sold under the trademark "GeoTech Drainage Panel" by GeoTech Systems, Inc., of McLean, VA, utilizes a core board made of bonded resin beads having water flow passages therebetween.
Many of the prior art drainage panels are adaptable to application on the inner side of shoring where such shoring is utilized to retain the earth wall of an excavation in a more nearly vertical orientation. This is believed to be common practice where limitations exist on the amount of land available for excavation. Where the shoring is left in place after an underground structure is built, backfill is placed between the panel covered shoring and the new construction. Sometimes, the panel covered shoring is used as a form against which concrete may be poured; thus leaving the panel in close contact with the newly built structure.
So far as is known, the drainage panels provided in the prior art have not functioned also as a waterproofing media. Their cores provide, at most, only one line of defense against leakage, and they are not equipped to provide waterproof joints between adjacent panels. Consequently, the practice has been to use these drainage panels in combination with previously known waterproofing systems such as bituminous coatings and others discussed above. The separate application of a water-proofing system and then a drainage system to the subterranean walls of the structure has proven to be relatively costly and time consuming.